Plasma physics is the field of physics which studies the dynamic behaviour of plasmas.

Briefly, it is the study of the statistical properties of a field of charged particles, called a plasma. Sometimes called "the fourth state of matter" (besides solid, liquid, and gas), plasma in this context refers to a gas that has been subjected to enough energy to dissociate atoms from their electrons (ionization), producing a cloud of ions and electrons. Because these particles are ionized (charged), the gas behaves in a different fashion than neutral gas in, for instance, the presence of electromagnetic fields.